Electronic properties of periodically modified graphene: A first-principles study*

Modifications of the geometric structure of pristine graphene should be a promising method to expand the possibility of application. We study the electronic properties of graphene with structural defects in the shape of truncated triangles arranged periodically in the framework of the density-functional theory. First, we consider systems in which defects are arranged in the same direction. In their energy band structures, one or more nearly flat bands appear at the Fermi energy. It is also found that the ground state of the system is ferromagnetic. Next, we consider systems in which additional triangular defects with the opposite direction are arranged. There are two defects in each unit cell and sides of regular triangles face each other. We find that all sysytems in this study can be semiconductors and the band gaps are tunable by changing the sizes of the defect and the unit cell. Interestingly, nearly flat bands sometimes appear at the valence band top and the conduction band bottom. We also discuss spatial distributions of the valence band top state and conduction band bottom state.